Electrosurgical tools have been characterized as monopolar or bipolar. Monopolar electrosurgery refers to a configuration where there is a separate return electrode connected to the patient, so that only one electrical pole is carried on the electrosurgical tool. In contrast, bipolar electrosurgery refers to a configuration where both electrical poles are carried on the surgical tool. Monopolar and bipolar electrosurgical tools each offer certain advantages and disadvantages to the surgeon.
One of the advantages of monopolar electrosurgical tools is that the surgeon can apply electrosurgical current whenever the conductive portion of the tool is in electrical contact with the patient. Thus, a surgeon may operate with monopolar electrosurgical tools from many different angles. In contrast, bipolar tools suffer from the drawback that the surgeon must carefully position the tool to ensure that both electrical poles are in electrical contact with the patient in order to apply electrosurgical current. This may limit the range of motion and the angle from which the surgeon can effectively use the bipolar tool.
Surgical shears, or scissors, have been designed for use with electrosurgical energy. The combination of scissors and electrosurgery allows the surgeon to mechanically cut tissue while coagulating the cut tissue using electrosurgical current. As the tissue is cut by the shearing surfaces, the cut tissue slides across the exterior surfaces of the shearing members where it is coagulated. Tissue may also be coagulated while it is being grasped by the scissors and prior to being mechanically cut. The exterior surfaces are the portions of each shearing member which are exposed when the shearing members are in a mated position. The exterior surfaces are generally opposite the shearing surfaces on each shearing member.
There are several variations of electrosurgical pole placement that allow electrosurgical current to flow through the cut tissue. For example, the exterior surface of one shearing member can be energized with a first pole, while the exterior surface of the other shearing member is energized with a second pole. In this configuration, electrosurgical current can flow from one exterior surface, through the cut tissue, to the other exterior surface.
In another example, both exterior surfaces are energized with a first pole, while both shearing surfaces are energized with a second pole. In this configuration, electrosurgical current can flow from each shearing surface, through the cut tissue, to an exterior surface. In both of these examples, it should be observed that each exterior surface is energized with only one electrical pole.
Surgeons often desire to use the scissors to coagulate bleeders without cutting tissue. It would be desirable to perform this function with the shearing members in a closed, or mated, position to avoid exposing the shearing edges. The availability of a coagulation feature on the scissors would avoid the need for a separate coagulation tool. The use of a separate coagulation tool requires the surgeon to switch tools in the middle of a procedure. This can be cumbersome in laparoscopic procedures.
It would be desirable to allow surgeons to use the exterior surfaces of the scissors to coagulate tissue. Presently available scissors have the disadvantage that the exterior surfaces can not be easily manipulated for purposes of coagulation because, as previously described, only one electrical pole is exposed to tissue on each exterior surface. In order to allow current to flow to the tissue, the surgeon must manipulate the scissors to contact both electrical poles to tissue. Thus, both exterior surfaces must be in contact with the tissue, or alternatively, an exterior surface and a shearing surface must contact tissue. These alternatives do not allow the convenience of simply contacting one exterior surface to the bleeding tissue.
U.S. Pat. No. 5,324,289 describes a bipolar surgical shearing instrument. One shearing member carries a first electrical pole, and a second shearing member carries a second electrical pole. At least one shearing surface and edge of the instrument is made from an electrically insulative material. This prevents the shears from creating an electrical short when the two shearing members are in contact. This design suffers from the drawback that only one electrical pole is exposed on each exterior surface. Thus, both shearing members must be in contact with the tissue of the patient in order to apply electrosurgical current.
U.S. Pat. No. 5,352,222 describes an improved bipolar surgical shearing instrument. The shearing surfaces and edges are metallic, thus improving the shearing action of the tool. The shearing surfaces and edges have a layer of electrical insulation which separates them from the electrodes. This design also has only one electrical pole exposed on each exterior surface. As with the previous design, both shearing members must be in electrical contact with the tissue in order to apply electrosurgical current.